1. Field of the Invention
The present invention relates to a method of producing an ethylene-propylene-diene copolymer, and more particularly, to a method of producing an ethylene-propylene-diene copolymer by using a metallocene compound found in the transition metal of the fourth group of the periodic table as a catalyst.
2. Description of the Related Art
Since the properties, such as thermostability, an antiweatherability, and an ozone resistance, of an ethylene-propylene-diene copolymer are superior to a styrene-butadiene rubber and a butadiene rubber, it is frequently used as a material in the fields of automobile, architecture, and industry. When conventionally producing the ethylene-propylene-diene compolymer, a so-called Ziegler-Natta catalyst system consisting of a vanadium compound as a main catalyst component and alkyl aluminum compound as a co-catalyst is in general use. When producing the ethylene-propylene-diene copolymer using the above method, a large quantity of catalyst should be used because the ability of the above catalyst is low. In addition, the stability of the catalyst at the reaction temperature of above 50° C. is deteriorated, and then the ability of the catalyst is rapidly decreased, so that there is a limit to the manufacturing process. In addition, the vanadium catalyst has multiple active sites according to the degree of the reduction by the alkyl aluminum co-catalyst, so that the composition distribution of the copolymer produced has not been uniform.
Recently, there are many examples of producing a ethylene-propylene-unconjugated diene copolymer by using the metallocene catalyst having high activity. However, most examples showed the method for copolymerizing by activating the metallocene compound as the main catalyst with a methyl aluminoxane as the co-catalyst. However, when using the above catalyst system, a larger quantity of the co-catalyst should be used, so that economically, the methods are not suitable. In addition, when the polymerization temperature is above 140° C., the activity of the catalyst is rapidly decreased, or the product having high molecule weight is difficulty produced due to the transition reaction of polymer chain by hydrogen located in a beta site of polymer chain from a catalytic metal during the polymerization.